Lithium-ion battery

ABSTRACT

A lithium-ion battery includes a positive electrode having an active material and a polymeric separator configured to allow electrolyte and lithium ions to flow between a first side of the separator and an opposite second side of the separator. The battery also includes a liquid electrolyte having a lithium salt dissolved in at least one non-aqueous solvent and a negative electrode having a lithium titanate active material. The positive electrode has a first capacity and the negative electrode has a second capacity that is less than the first capacity.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent applicationSer. No. 10/979,040 filed Oct. 29, 2004 (now U.S. Pat. No. 7,811,705)and is also a Continuation of U.S. patent application Ser. No.10/978,712 filed Oct. 29, 2004 (now U.S. Pat. No. 7,682,745). The entiredisclosures of U.S. patent application Ser. No. 10/979,040 and U.S.patent application Ser. No. 10/978,712 (now U.S. Pat. No. 7,682,745) areincorporated herein by reference.

BACKGROUND

The present invention relates generally to the field of lithium-ionbatteries. Specifically, the present invention relates to lithium-ionbatteries that are relatively tolerant to over-discharge conditions.

Lithium-ion batteries include a positive current collector (e.g.,aluminum such as an aluminum foil) having an active material providedthereon (e.g., LiCoO₂) and a negative current collector (e.g., coppersuch as a copper foil) having an active material (e.g., a carbonaceousmaterial such as graphite) provided thereon. Together the positivecurrent collector and the active material provided thereon are referredto as a positive electrode, while the negative current collector and theactive material provided thereon are referred to as a negativeelectrode.

FIG. 1 shows a schematic representation of a portion of a lithium-ionbattery 10 such as that described above. The battery 10 includes apositive electrode 20 that includes a positive current collector 22 anda positive active material 24, a negative electrode 30 that includes anegative current collector 32 and a negative active material 34, anelectrolyte material 40, and a separator (e.g., a polymeric microporousseparator, not shown) provided intermediate or between the positiveelectrode 20 and the negative electrode 30. The electrodes 20, 30 may beprovided as relatively flat or planar plates or may be wrapped or woundin a spiral or other configuration (e.g., an oval configuration). Theelectrode may also be provided in a folded configuration.

During charging and discharging of the battery 10, lithium ions movebetween the positive electrode 20 and the negative electrode 30. Forexample, when the battery 10 is discharged, lithium ions flow from thenegative electrode 30 to the to the positive electrode 20. In contrast,when the battery 10 is charged, lithium ions flow from the positiveelectrode 20 to the negative electrode 30.

FIG. 2 is a graph 100 illustrating the theoretical charging anddischarging behavior for a conventional lithium-ion battery. Curve 110represents the electrode potential versus a lithium reference electrodefor a positive electrode that includes an aluminum current collectorhaving a LiCoO₂ active material provided thereon, while curve 120represents the electrode potential versus a lithium reference electrodefor a negative electrode that includes a copper current collector havinga carbonaceous active material provided thereon. The difference betweencurves 110 and 120 is representative of the overall cell voltage.

As shown in FIG. 2, upon initial charging to full capacity, thepotential of the positive electrode, as shown by curve 110, increasesfrom approximately 3.0 volts to a point above the corrosion potential ofcopper used to form the negative electrode (designated by dashed line122). The potential of the negative electrode decreases fromapproximately 3.0 volts to a point below the decomposition potential ofthe LiCoO₂ active material provided on the aluminum current collector(designated by dashed line 112). Upon initial charging, the batteryexperiences an irreversible loss of capacity due to the formation of apassive layer on the negative current collector, which may be referredto as a solid-electrolyte interface (“SEI”). The irreversible loss ofcapacity is shown as a ledge or shelf 124 in curve 120.

One difficulty with conventional lithium-ion batteries is that when sucha battery is discharged to a point near zero volts, it may exhibit aloss of deliverable capacity and corrosion of the negative electrodecurrent collector (copper) and possibly of the battery case, dependingon the material used and the polarity of the case. As shown in FIG. 2,after initial charging of the battery, a subsequent discharge of thebattery in which the voltage of the battery approaches zero volts (i.e.,zero percent capacity) results in a negative electrode potential thatfollows a path designated by dashed line 126. As shown in FIG. 2, thenegative electrode potential levels off or plateaus at the coppercorrosion potential of the negative current collector (approximately 3.5volts for copper and designated by dashed line 122 in FIG. 2).

The point at which the curves 110 and 120 cross is sometimes referred toas the zero voltage crossing potential, and corresponds to a cellvoltage that is equal to zero (i.e., the difference between the twocurves equals zero at this point). Because of the degradation of thecopper current collector which occurs at the copper corrosion potential,the copper material used for the negative current collector corrodesbefore the cell reaches a zero voltage condition, resulting in a batterythat exhibits a loss of deliverable capacity.

While FIG. 2 shows the theoretical charging and discharging behavior ofa battery that may experience corrosion of the negative currentcollector when the battery approaches a zero voltage configuration, itshould be noted that there may also be cases in which the activematerial on the positive current collector may degrade innear-zero-voltage conditions. In such cases, the theoretical chargingand discharging potential of the positive electrode versus a lithiumreference electrode would decrease to the decomposition potential of thepositive active material (shown as line 112 in FIG. 2), at which pointthe positive active material would decompose, resulting in potentiallydecreased protection against future over-discharge conditions.

Because damage to the lithium-ion battery may occur in the event of alow voltage condition, conventional lithium-ion batteries may includeprotection circuitry and/or may be utilized in devices that includeprotection circuitry which substantially reduces the current drain fromthe battery (e.g., by disconnecting the battery).

The medical device industry produces a wide variety of electronic andmechanical devices for treating patient medical conditions. Dependingupon the medical condition, medical devices can be surgically implantedor connected externally to the patient receiving treatment. Cliniciansuse medical devices alone or in combination with drug therapies andsurgery to treat patient medical conditions. For some medicalconditions, medical devices provide the best, and sometimes the only,therapy to restore an individual to a more healthful condition and afuller life.

It may be desirable to provide a source of battery power for suchmedical devices, including implantable medical devices. In such cases,it may be advantageous to provide a battery that may be recharged. Itmay also be advantageous to provide a battery that may be discharged toa near zero voltage condition without substantial risk that the batterymay be damaged (e.g., without corroding one of the electrodes or thebattery case, decomposing the positive active material, etc.) such thatthe performance of the battery is degraded in subsequent charging anddischarging operations.

It would be advantageous to provide a battery (e.g., a lithium-ionbattery) that may be discharged to near zero volts without producing asubsequent decrease in the amount of deliverable capacity or producing acorroded negative electrode or battery case. It would also beadvantageous to provide a battery that compensates for the irreversibleloss of capacity resulting from initial charging of the battery to allowthe battery to be used in near zero voltage conditions withoutsignificant degradation to battery performance. It would also beadvantageous to provide a medical device (e.g., an implantable medicaldevice) that utilizes a battery that includes any one or more of theseor other advantageous features.

SUMMARY

An exemplary embodiment relates to a lithium-ion battery comprising apositive electrode comprising an active material and a polymericseparator configured to allow electrolyte and lithium ions to flowbetween a first side of the separator and an opposite second side of theseparator. The battery also comprises a liquid electrolyte comprising alithium salt dissolved in at least one non-aqueous solvent and anegative electrode comprising a lithium titanate active material. Thepositive electrode has a first capacity and the negative electrode has asecond capacity that is less than the first capacity.

Another exemplary embodiment relates to a lithium-ion battery comprisinga positive electrode having a first capacity and comprising a foilcurrent collector and an active material comprising at least onematerial selected from the group consisting of LiCoO₂, LiMn₂O₄,LiCo_(x)Ni_((1−x))O₂ where x is between approximately 0.05 and 0.8,LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂, LiAl_(x)Co_(y)Ni_((1−x−y))O₂ where x isbetween approximately 0.05 and 0.3 and y is between approximately 0.1and 0.3, and LiTi_(x)Co_(y)Ni_((1−x−y))O₂ where x is betweenapproximately 0.05 and 0.3 and y is between approximately 0.1 and 0.3.The battery also includes an electrolyte and a negative electrode havinga second capacity that is not greater than the first capacity, thenegative electrode comprising a foil current collector and a lithiumtitanate active material.

Another exemplary embodiment relates to a lithium-ion battery comprisinga positive electrode having a first capacity and comprising a foilcurrent collector and an active material comprising at least onematerial selected from the group consisting of LiCoO₂, LiMn₂O₄,LiCo_(x)Ni_((1−x))O₂ where x is between approximately 0.05 and 0.8,LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂, LiAl_(x)Co_(y)Ni_((1−x−y))O₂ where x isbetween approximately 0.05 and 0.3 and y is between approximately 0.1and 0.3, and LiTi_(x)Co_(y)Ni_((1−x−y))O₂ where x is betweenapproximately 0.05 and 0.3 and y is between approximately 0.1 and 0.3.The battery also includes a liquid electrolyte and a negative electrodehaving a second capacity that is not greater than the first capacity.The negative electrode comprises a foil current collector and aLi₄Ti₅O₁₂ active material. A porous polymeric separator is providedbetween the positive electrode and the negative electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a conventional lithium-ionbattery.

FIG. 2 is a graph illustrating the theoretical charging and dischargingbehavior for a conventional lithium-ion battery such as that shownschematically in FIG. 1.

FIG. 3 is a schematic cross-sectional view of a portion of a lithium-ionbattery according to an exemplary embodiment.

FIG. 4 is a graph illustrating the theoretical charging and dischargingbehavior for a lithium-ion battery such as that shown in FIG. 3.

FIG. 5 is a graph illustrating the discharge capacity of battery cellsand the effect of overdischarge cycling of such cells.

FIG. 6 is a graph illustrating voltage traces for a cell using aLi₄Ti₅O₁₂ active material on an aluminum negative current collector.

FIG. 7 is a graph illustrating voltage traces for a comparative cellusing a carbon active material on a copper negative current collector.

FIG. 8 is a schematic view of a system in the form of an implantablemedical device implanted within a body or torso of a patient.

FIG. 9 is schematic view of another system in the form of an implantablemedical device.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

With reference to FIG. 3, a schematic cross-sectional view of a portionof a lithium-ion battery 200 is shown according to an exemplaryembodiment. According to an exemplary embodiment, the battery 200 has arating of between approximately 10 and 1000 milliampere hours (mAh).According to another exemplary embodiment, the battery has a rating ofbetween approximately 100 and 400 mAh. According to another exemplaryembodiment, the battery is an approximately 300 mAh battery. Accordingto another exemplary embodiment, the battery is an approximately 75 mAhbattery.

The battery 200 includes at least one positive electrode 210 and atleast one negative electrode 220. The electrodes may be provided as flator planar components of the battery 200, may be wound in a spiral orother configuration, or may be provided in a folded configuration. Forexample, the electrodes may be wrapped around a relatively rectangularmandrel such that they form an oval wound coil for insertion into arelatively prismatic battery case. According to other exemplaryembodiments, the battery may be provided as a button cell battery, athin film solid state battery, or as another lithium-ion batteryconfiguration.

The battery case (not shown) may be made of a metal such as aluminum oran aluminum alloy or another metal. According to an exemplaryembodiment, the battery case may be made of titanium, a titanium alloy,or stainless steel. According to another exemplary embodiment, thebattery case may be made of a plastic material or a plastic-foillaminate material (e.g., an aluminum foil provided intermediate apolyolefin layer and a polyester layer).

According to an exemplary embodiment, the negative electrode is coupledto an aluminum case by a member or tab comprising aluminum or analuminum alloy. An aluminum or aluminum alloy member or tab may becoupled or attached to the positive electrode. The tabs may serve asterminals for the battery according to an exemplary embodiment.

The dimensions of the battery 200 may differ according to a variety ofexemplary embodiments. For example, according to one exemplaryembodiment in which the electrodes are wound such that they may beprovided in a relatively prismatic battery case, the battery hasdimensions of between approximately 30-40 mm by between approximately20-30 mm by between approximately 5-7 mm. According to another exemplaryembodiment, the dimensions of the battery are approximately 20 mm by 20mm by 3 mm. According to another exemplary embodiment, a battery may beprovided in the form of a button cell type battery having a diameter ofapproximately 30 mm and a thickness of approximately 3 mm. It will beappreciated by those of skill in the art that such dimensions andconfigurations as are described herein are illustrative only, and thatbatteries in a wide variety of sizes, shapes, and configurations may beproduced in accordance with the novel concepts described herein.

An electrolyte 230 is provided intermediate or between the positive andnegative electrodes to provide a medium through which lithium ions maytravel. The electrolyte may be a liquid (e.g., a lithium salt dissolvedin one or more non-aqueous solvents). According to an exemplaryembodiment, the electrolyte may be a mixture of polycarbonate (PC) and a1.0 M salt of LiPF₆. According to another exemplary embodiment, anelectrolyte may be used that is free of ethylene carbonate, vinylenecarbonate or a lithium bis-oxalatoborate salt (sometimes referred to asLiBOB) that may be used in conventional lithium batteries.

Various other electrolytes may be used according to other exemplaryembodiments. According to an exemplary embodiment, the electrolyte maybe a lithium salt dissolved in a polymeric material such aspoly(ethylene oxide) or silicone. According to another exemplaryembodiment, the electrolyte may be an ionic liquid such asN-methyl-N-alkylpyrrolidinium bis(trifluoromethanesulfonyl)imide salts.According to another exemplary embodiment, the electrolyte may be asolid state electrolyte such as a lithium-ion conducting glass such aslithium phosphorous oxynitride (LiPON). According to another exemplaryembodiment, the electrolyte may be a 1:1 mixture of ethylene carbonateto diethylene carbonate (EC:DEC) in a 1.0 M salt of LiPF₆. According toanother exemplary embodiment, the electrolyte may include apolypropylene carbonate solvent and a lithium bis-oxalatoborate salt.According to other exemplary embodiments, the electrolyte may compriseone or more of a PVDF copolymer, a PVDF-polyimide material, andorganosilicon polymer, a thermal polymerization gel, a radiation curedacrylate, a particulate with polymer gel, an inorganic gel polymerelectrolyte, an inorganic gel-polymer electrolyte, a PVDF gel,polyethylene oxide (PEO), a glass ceramic electrolyte, phosphateglasses, lithium conducting glasses, lithium conducting ceramics, and aninorganic ionic liquid gel, among others.

A separator 250 is provided intermediate or between the positiveelectrode 210 and the negative electrode 220. According to an exemplaryembodiment, the separator 250 is a polymeric material such as apolypropylene/polyethelene copolymer or another polyolefin multilayerlaminate that includes micropores formed therein to allow electrolyteand lithium ions to flow from one side of the separator to the other.The thickness of the separator 250 is between approximately 10micrometers (μm) and 50 μm according to an exemplary embodiment.According to a particular exemplary embodiment, the thickness of theseparator is approximately 25 μm and the average pore size of theseparator is between approximately 0.02 μm and 0.1 μm.

The positive electrode 210 includes a current collector 212 made of aconductive material such as a metal. According to an exemplaryembodiment, the current collector 212 comprises aluminum or an aluminumalloy.

According to an exemplary embodiment, the thickness of the currentcollector 212 is between approximately 5 μm and 75 μm. According to aparticular exemplary embodiment, the thickness of the current collector212 is approximately 20 μm. It should also be noted that while thepositive current collector 212 has been illustrated and described asbeing a thin foil material, the positive current collector may have anyof a variety of other configurations according to various exemplaryembodiments. For example, the positive current collector may be a gridsuch as a mesh grid, an expanded metal grid, a photochemically etchedgrid, or the like.

The current collector 212 has a layer of active material 216 providedthereon (e.g., coated on the current collector). While FIG. 3 shows thatthe active material 216 is provided on only one side of the currentcollector 212, it should be understood that a layer of active materialsimilar or identical to that shown as active material 216 may beprovided or coated on both sides of the current collector 212.

According to an exemplary embodiment, the active material 216 is amaterial or compound that includes lithium. The lithium included in theprimary active material 216 may be doped and undoped during dischargingand charging of the battery, respectively. According to an exemplaryembodiment, the primary active material 216 is lithium cobalt oxide(LiCoO₂). According to another exemplary embodiment, the active materialprovided on the current collector 212 is LiMn₂O₄. According to anotherexemplary embodiment, the active material provided on the currentcollector 212 is a material of the form LiCo_(x)Ni_((1−x))O₂, where x isbetween approximately 0.05 and 0.8. According to another exemplaryembodiment, the active material provided on the current collector 212 isa material of the form LiNi_(x)Co_(y)Mn_((1−x−y))O₂ (e.g.,LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂). According to another exemplaryembodiment, the active material provided on the current collector 212 isa metal-doped variety of one of these materials, such as a material ofthe form LiM_(x)Co_(y)Ni_((1−x−y))O₂, where M is aluminum or titaniumand x is between approximately 0.05 and 0.3 and y is betweenapproximately 0.1 and 0.3.

For certain applications, it may be desirable to provide a batteryhaving a cell voltage of greater than approximately 3 volts. In suchcases, a higher-voltage active material may be utilized on the positivecurrent collector, such as a material in the formLi_(2−x)Co_(y)Fe_(z)Mn_(4−(y+z))O₈ (e.g.,Li₂Co_(0.4)Fe_(0.4)Mn_(3.2)O₈). It is believed that such an activematerial may charge up to 5.2 volts versus a lithium referenceelectrode, making it possible to obtain an overall cell voltage of up toapproximately 3.7 volts. Other relatively high-voltage active materialsthat may be used for the positive electrode include LiCoPO₄; Li₂CoPO₄F;LiNiPO₄; Li[Ni_(0.2)Li_(0.2)Mn_(0.6)]O₂; and LiCo_(x)Mn_(2−x)O₄ (e.g.,LiCu_(0.3)Mn_(1.7)O₄).

According to various other exemplary embodiments, the active materialmay include a material such as a material of the form Li_(1−x)MO₂ whereM is a metal (e.g., LiCoO₂, LiNiO₂, and LiMnO₂), a material of the formLi_(1−w)(M′_(x)M″_(y))O₂ where M′ and M″ are different metals (e.g.,Li(Cr_(x)Mn_(1−x))O₂, Li(Al_(x)Mn_(1−x))O₂, Li(Co_(x)M_(1−x))O₂ where Mis a metal, Li(Co_(x)Ni_(1−x))O₂, and Li(Co_(x)Fe_(1−x))O₂)), a materialof the form L_(1−w)(Mn_(x)Ni_(y)CO_(z))O₂ (e.g.,Li(Mn_(1/3)Ni_(1/3)Co_(1/3))O₂, Li(Mn_(1/3)Ni_(1/3)Co_(1/3−x)Mg_(x))O₂,Li(Mn_(0.4)Ni_(0.4)CO_(0.2))O₂, and Li(Mn_(0.1)Ni_(0.1)Co_(0.8))O₂), amaterial of the form Li_(1−w)(Mn_(x)Ni_(x)Co_(1-2x))O₂, a material ofthe form Li_(1−W)(Mn_(x)Ni_(y)Co_(z)Al_(w))O₂, a material of the formLi_(1-w)(Ni_(x)Co_(y)Al_(z))O₂ (e.g., Li(Ni_(0.8)Co_(0.15)Al_(0.05))O₂),a material of the form Li_(1−w)(Ni_(x)Co_(y)M_(z))O₂ where M is a metal,a material of the form Li_(1−W)(Ni_(x)Mn_(y)M_(z))O₂ where M is a metal,a material of the form Li(Ni_(x−y)Mn_(y)Cr_(2−x))O₄, LiMn₂O₄, a materialof the form LiM′M″₂O₄ where M′ and M″ are different metals (e.g.,LiMn_(2−y−z), Ni_(y)O₄, Li_(z)O₄, LiMn_(1.5) Ni_(0.5)O₄, LiNiCuO₄,LiMn_(1−x)Al_(x)O₄, LiNi_(0.5)Ti_(0.5)O₄, andLi_(1.05)Al_(0.1)Mn_(1.85)O_(4−z)F_(z)), Li₂MnO₃, a material of the formLi_(x)V_(y)O_(z) (e.g., LiV₃O₈, LiV₂O₅, and LiV₆O₁₃), a material of theform LiMPO₄ where M is a metal or LiM_(x)′M″_(1−x)PO₄ where M′ and M″are different metals (e.g., LiFePO₄, LiFe_(x)M_(1−x)PO₄ where M is ametal, LiVOPO₄, and Li₃V₂(PO₄)₃, and LiMPO_(4x) where M is a metal suchas iron or vanadium and X is a halogen such as fluorine, andcombinations thereof.

A binder material may also be utilized in conjunction with the layer ofactive material 216 to bond or hold the various electrode componentstogether. For example, according to an exemplary embodiment, the layerof active material may include a conductive additive such as carbonblack and a binder such as polyvinylidine fluoride (PVDF) or anelastomeric polymer.

According to an exemplary embodiment, the thickness of the layer ofactive material 216 is between approximately 0.1 μm and 3 mm. Accordingto another exemplary embodiment, the thickness of the layer of activematerial 216 is between approximately 25 μm and 300 μm. According to aparticular exemplary embodiment, the thickness of the layer of activematerial 216 is approximately 75 μm.

The negative electrode 220 includes a current collector 222 that is madeof a conductive material such as a metal. According to an exemplaryembodiment, the current collector 222 is aluminum or an aluminum alloy.One advantageous feature of utilizing an aluminum or aluminum alloycurrent collector is that such a material is relatively inexpensive andmay be relatively easily formed into a current collector. Otheradvantageous features of utilizing an aluminum or aluminum currentcollector is that such a material may exhibit a relatively low density,a relatively high conductivity, is relatively readily weldable, and isgenerally commercially available. According to another exemplaryembodiment, the current collector 222 is titanium or a titanium alloy.According to another exemplary embodiment, the current collector 222 issilver or a silver alloy.

While the negative current collector 222 has been illustrated anddescribed as being a thin foil material, the negative current collectormay have any of a variety of other configurations according to variousexemplary embodiments. For example, the negative current collector maybe a grid such as a mesh grid, an expanded metal grid, a photochemicallyetched grid, or the like.

According to an exemplary embodiment, the thickness of the currentcollector 222 is between approximately 100 nm and 100 μm. According toanother exemplary embodiment, the thickness of the current collector 222is between approximately 5 μm and 25 μm. According to a particularexemplary embodiment, the thickness of the current collector 222 isapproximately 10 μm.

The negative current collector 222 has an active material 224 providedthereon. While FIG. 3 shows that the active material 224 is provided ononly one side of the current collector 222, it should be understood thata layer of active material similar or identical to that shown may beprovided or coated on both sides of the current collector 222.

According to an exemplary embodiment, the negative active material 224is a lithium titanate material such as Li₄Ti₅O₁₂ (sometimes referred toas Li_(1+x)[Li_(1/3)Ti_(5/3)]O₄, with 0≦x<1). Other lithium titanatematerials which may be suitable for use as the negative active materialmay include one or more of the following lithium titanate spinelmaterials: H_(x)Li_(y−x)TiO_(x)O₄, H_(x)Li_(y−x)TiO_(x)O₄,Li₄M_(x)Ti_(5−x)O₁₂, Li_(x)Ti_(y)O₄, Li_(x)Ti_(y)O₄,Li₄[Ti_(1.67)Li_(0.33−y)M_(y)]O₄, Li₂TiO₃, Li₄Ti_(4.75)V_(0.25)O₁₂,Li₄Ti_(4.75)Fe_(0.25)O_(11.88), Li₄Ti_(4.5)Mn_(0.5)O₁₂, and LiM′M″XO₄(where M′ is a metal such as nickel, cobalt, iron, manganese, vanadium,copper, chromium, molybdenum, niobium, or combinations thereof, M″ is anoptional three valent non-transition metal, and X is zirconium,titanium, or a combination of these two). Note that such lithiumtitanate spinel materials may be used in any state of lithiation (e.g.,Li_(4+x)Ti₅O₁₂, where 0≦x≦3).

A binder material may also be utilized in conjunction with the layer ofactive material 224. For example, according to an exemplary embodiment,the layer of active material may include a binder such as polyvinylidinefluoride (PVDF) or an elastomeric polymer. The active material 224 mayalso include a conductive material such as carbon (e.g., carbon black)at weight loadings of between zero and ten percent to provide increasedelectronic conductivity.

According to various exemplary embodiments, the thickness of the activematerial 224 is between approximately 0.1 μm and 3 mm. According toother exemplary embodiments, the thickness of the active material 224may be between approximately 25 μm and 300 μm. According to anotherexemplary embodiment, the thickness of the active material 224 may bebetween approximately 20 μm and 90 μm, and according to a particularexemplary embodiment, approximately 75 μm.

FIG. 4 is a graph 300 illustrating the theoretical charging anddischarging behavior for a lithium-ion battery constructed in accordancewith an exemplary embodiment such as that shown and described withregard to FIG. 3. Curve 310 represents the electrode potential versus alithium reference electrode for a positive electrode (e.g., positiveelectrode 210) that includes an aluminum current collector having aLiCoO₂ primary active material provided thereon.

Curve 320 represents the electrode potential versus a lithium referenceelectrode for a negative electrode that includes an aluminum currentcollector having a lithium titanate active material provided thereon.The difference between curves 310 and 320 is representative of theoverall cell voltage of the battery, and is represented as curve 340 inFIG. 4.

As shown in FIG. 4, the relatively flat portion (labeled with referencenumeral 324) of the curve 320 representing the voltage of the negativeelectrode (e.g., electrode 220) is at a level of between approximately1.5 and 1.6 volts. Thus, the relatively flat portion 324 of the curve320 is at a level that is significantly greater than that of anelectrode utilizing a carbon active material (see, e.g., curve 120 inFIG. 2, which represents the theoretical voltage versus a lithiumreference electrode for a negative electrode incorporating a carbonactive material).

When the cell is charged, the potentials of the positive and negativeelectrodes progress to the right along curves 310 and 320, respectively.When the cell is discharged, the potentials of the positive and negativeelectrode potentials progress toward the left along curves 310 and 320,respectively, with a zero voltage crossing potential of approximately3.8 volts (shown as point 330 in FIG. 4). As the cell approaches a zerovoltage condition (e.g., curve 340 drops to zero volts, representing thevoltage differential between the positive and negative electrodes), thevoltage of the positive electrode is above the decomposition potentialof the LiCoO₂ active material provided thereon, which is shown as dashedline 322 in FIG. 4. Additionally, because an aluminum current collectoris utilized for the negative electrode, the negative electrode hasincreased resistance to corrosion as compared to copper materials whichmay be utilized for the negative electrode.

It is intended that a lithium-ion battery such as that described hereinmay be fully discharged while the materials for both electrodes,including their corresponding current collectors, are stable (e.g.,corrosion of the current collectors and/or the decomposition of activematerial may be avoided, etc.). For example, it is intended that abattery produced using a positive electrode including an aluminumcurrent collector and a LiCoO₂ active material and a negative electrodeincluding an aluminum current collector and a lithium titanate activematerial will allow for repeated cycling of the battery to zero ornear-zero voltage conditions without a significant decline in batterycharging capacity or battery performance. One potential advantageousfeature of such an arrangement is that the occurrence of reduced devicefunctionality (i.e., the need to recharge more frequently) and corrosionof the current collectors and battery case (with the incumbentpossibility of leaking potentially corrosive and toxic battery contents)may be reduced or avoided.

Various advantageous features may be obtained by batteries such as thoseshown and described herein. For example, use of batteries which utilizea lithium titanate active material on an aluminum electrode mayeliminate the need to utilize circuitry to disconnect batteriesapproaching near-zero voltage conditions, since such batteries may becycled to zero voltage and near-zero voltage repeatedly without asignificant loss in battery performance or capacity. By not utilizingcircuitry for this function, volume and cost reductions may be obtained.

One advantageous feature of using a lithium titanate material is that itis believed that when used in a negative electrode of a lithium-ionbattery, such materials will cycle lithium at a potential plateau ofabout 1.55 volts versus a lithium reference electrode. This issubstantially higher than graphitic carbon, which cycles lithium atapproximately 0.1 volts in the fully charged state (see, e.g., FIG. 2,in which curve 120 is representative of the charging/dischargingbehavior of a negative electrode utilizing graphitic carbon). As aresult, the battery using lithium titanate is believed to be less likelyto result in plating of lithium (which occurs at 0 volts versus alithium reference) while being charged. Lithium plating is a well-knownphenomenon that can lead to loss in performance of lithium ionbatteries.

Another advantage of using a lithium titanate material instead of acarbonaceous material for the negative active material is that it isbelieved that the use of a lithium titanate material allows for chargingand discharging of the battery at higher rates than is capable usingcarbonaceous materials. For example, a common upper limit for the rateof charge in lithium ion batteries is about 1 C (meaning that thebattery can be fully charged from the discharged state in one hour).Conversely, it has been reported in literature that lithium titanate maybe charged at rates up to 10 C (i.e., attaining full charge in 1/10hour, or six minutes). One potential reason for this is that negativeelectrodes utilizing a lithium titanate active material are believed tobe less susceptible to the risk of lithium plating. The ability torecharge a battery more quickly may substantially increase thefunctionality of devices that employ such a battery.

It is also believed that the use of negative electrodes that include alithium titanate active material may allow for charging of the batteryat voltages that exceed those used in the charging of batteries in whichthe negative electrodes utilize carbon active materials. One potentialadvantage of such a property is that nonhermetic cells (e.g., cellsusing a rivet polymer feedthrough, foil package, etc.) may be produced.Nonhermetic cells typically have greater energy density than othercells, are relatively inexpensive to manufacture, and may be producedusing a wider variety of materials (e.g, polymer foil laminates, etc.).In medical applications in particular, such cells have conventionallyutilized with polymer or gel electrolytes which have lower vaporpressure to provide a reduced risk of leakage. However, suchelectrolytes are typically less conductive than liquid electrolytes,resulting in relatively low power and/or charge rate. By utilizing abattery that includes a lithium titanate active material on an aluminumcurrent collector, the charge voltage of the cell may be increased tocompensate for resistive losses (e.g., IR drops) in the electrolyte.

Lithium titanate materials are also believed to offer superior cyclelife because they are so called “zero-strain” materials. Zero strainmaterials have crystal lattices which do not experience shrinkage orcontraction with lithium doping/de-doping, making them free fromstrain-related degradation mechanisms. Such materials also have arelatively high specific capacity (approximately 155 mAh/g) and asimilar volumetric capacity density to graphitic carbon.

A further advantage of the higher potential of the lithium titanatematerial is that it avoids decomposition of organic solvents (such aspropylene carbonate) commonly used in lithium ion batteries. In sodoing, it may reduce negative consequences such as formation of gas,cell swelling, and reduction of reversible battery capacity.

Another potential advantageous feature of utilizing a lithium titanatematerial for the negative electrode active material is that morefavorable design rules may be possible. For example, in conventionallithium-ion cells, the negative electrode must overlap the positiveelectrode by approximately 1 mm on all edges in order to avoid platingof lithium. For applications in which space is a concern, this mayresult in significant wasted volume (e.g., for a cranial implant cellthat is approximately 22 mm high, this may result in wasted volume ofapproximately 10 percent). Because use of a titanate material reducesthe risk of lithium plating, it is believed that the design requirementof overlapping positive and negative electrodes may be unnecessary, thusallowing the production of lithium-ion batteries with improved energydensity.

The lithium diffusion coefficient for lithium titanate materials may beon the order of approximately 2×10⁻⁸ cm²/s, which is approximately tentimes that of carbon, thus allowing a comparatively rapid sustained ratecapability. The use of such materials may allow the manufacture ofbatteries having lower surface area electrodes while still achievingadequate power and recharge rates. According to an exemplary embodiment,a battery utilizes monolithic (i.e., single-plate) electrodes in a coincell or a foil laminate package. Due to the comparatively rapidsustained rate capability of the lithium titanate material, the batterymay be relatively thin (e.g., approximately 1 mm) and inexpensive.Further, according to other exemplary embodiments, batteries may beproduced in contoured shapes, which may allow for packaging of suchbatteries unobtrusively and in unconventional ways in a device (such asalong an inner surface of a device housing or case, such as the housingor case of a medical device such as a pacemaker). This may be especiallyadvantageous in a device such as a cranial implant, where it may bedesirable to provide the device having a contour to match the curvatureof the skull.

Conventional lithium-ion cells are balanced with a nominal excessnegative active material of between approximately five and ten percentto avoid plating of lithium. The use of excess active material resultsin a larger battery, which results in a cell having reduced energydensity. According to an exemplary embodiment, a battery or cell using alithium titanate active material on an aluminum negative currentcollector may be produced without excess negative active material (e.g.,as a “balanced design”).

Comparative Example #1

This example illustrates the overdischarge performance of lithium ionbatteries utilizing a negative electrode having Li₄Ti₅O₁₂ activematerial coated onto an aluminum current collector as compared to theperformance of lithium ion batteries in which a carbon active material(graphitized MCMB) is coated onto a copper current collector. In allcases, the electrodes were cycled against positive electrodes having aLiCoO₂ active material with a capacity of 5.53 mAh coated on an aluminumcurrent collector.

Negative electrodes were produced by mixing lithium titanate(commercially available from Süd Chemie Corporation) with apoly(vinylidine fluoride) binder, carbon black and 1-methyl-2-pyrolidone(NMP) into a slurry and depositing the mixture onto an aluminum foilcurrent collector and drying on a heated drum. The active weight percentof the dried coating was 89.25%. Three coating deposition levels of thecoating were used: 17.37, 18.78 and 20.69 mg/cm². Based on thetheoretical specific capacity of Li₄Ti₅O₁₂ (155 mAh/g), the capacity ofthese electrodes was 4.76, 5.14 and 5.67 mAh, respectively. Thus, whencycled against the positive electrodes, the cell balance (i.e., theratio of the negative and positive electrode capacities) was 0.85, 0.93and 1.02, respectively.

After drying, the electrode coatings were calendared to a density ofabout 2.2 g/cm³ and cut into circular disks having an area of 1.98 cm².Lithium ion cells were produced by assembling these electrodes intotype-2032 coin cell hardware. A microporous polyolefin separator wasused to separate the negative and positive electrodes, and the cellswere activated by the addition of electrolyte consisting of 1 M LiPF₆ ina mixture of propylene carbonate, ethylene carbonate and diethylcarbonate.

Comparative cells were manufactured in identical fashion, with theexception of the fact that the negative electrodes utilized graphiteactive material (mesocarbon microbeads) coated on copper foil.

Cells were charged and discharged at a rate of 0.2 mA using an ARBINBT2000 battery cycler. For the first four cycles, the cells were cycledover a normal operating voltage range (3.0 to 1.8 V for the Li₄Ti₅O₁₂cells, 4.075 to 2.75 volts for the comparative cells). After completingfour cycles, the cells then underwent four overdischarge cycles, wherethey were discharged to 0 volts and charged back to their normal chargevoltage. The overdischarge took place as a sequence of steps atprogressively lower currents: 0.2 mA down to 1.8 volts, 0.05 mA to 1.0volts and 0.01 mA to 0 volts. Following the overdischarge cycles, thecells were then cycled over the original voltage range to measure therecovered capacity for the cells.

A graph showing the discharge capacity versus cycle number for each ofthe cells tested is shown in FIG. 5. Test data revealed a loss ofdischarge capacity over time after repeated overdischarge cycling forthe comparative cells (i.e., cells using carbon active material oncopper current collectors), while little or no loss of dischargecapacity was observed for cells utilizing Li₄Ti₅O₁₂ negative activematerial and an aluminum foil current collector.

TABLE 1 lists the cell discharge capacity of the cells during the fourthand ninth cycles of testing (i.e., the cycles immediately preceding andimmediately following the overdischarge cycles). For cells usingnegative electrodes with a Li₄Ti₅O₁₂ active material on an aluminumcurrent collector, there is little or no loss in capacity following theoverdischarge cycles. For the comparative cells (graphite activematerial on copper current collector), the average capacity loss wasobserved to be 84%.

TABLE 1 also lists the ratio of theoretical capacity of the negative andpositive electrodes for the Li₄Ti₅O₁₂ cells. This data indicates thatlittle or no capacity loss may be obtained regardless of whether thecells are negative limited (ratio of negative to positive electrodecapacity less than 1) or positive limited (ratio of negative to positiveelectrode capacity greater than 1).

TABLE 1 Negative/Positive Cycle 4 Cycle 9 Negative Electrode CapacityDischarge Discharge Capacity Loss Group/Serial Active Ratio for CapacityCapacity Due to Number Material Li₄Ti₅O₁₂ Cells (mAh) (mAh)Overdischarge 17-CAL-01 Li₄Ti₅O₁₂ 0.86 4.12 4.13 −0.3% 17-CAL-02Li₄Ti₅O₁₂ 0.86 4.37 4.40 −0.6% 17-CAL-03 Li₄Ti₅O₁₂ 0.86 4.49 4.47 0.4%Average 4.33 4.33 −0.2% Standard Dev. 0.19 0.18 0.5% 19-CAL-01 Li₄Ti₅O₁₂0.93 4.81 4.83 −0.4% 19-CAL-02 Li₄Ti₅O₁₂ 0.93 4.36 4.40 −0.8% 19-CAL-03Li₄Ti₅O₁₂ 0.93 4.84 4.78 1.2% Average 4.67 4.67 0.0% Standard Dev. 0.270.24 1.1% 21-CAL-02 Li₄Ti₅O₁₂ 1.02 5.32 5.32 0.1% 21-CAL-03 Li₄Ti₅O₁₂1.02 4.37 4.23 3.2% Average 4.84 4.77 1.6% Standard Dev. 0.67 0.77 2.2%MCMB-02 Carbon n/a 4.99 1.68 66.4% MCMB-03 Carbon n/a 4.96 1.44 71.0%MCMB-04 Carbon n/a 4.88 0.14 97.1% MCMB-05 Carbon n/a 4.91 0.72 85.3%MCMB-06 Carbon n/a 4.88 0.00 100.0% Average 4.93 0.80 84.0% StandardDev. 0.05 0.75 15.1%

Comparative Example #2

This example illustrates potential advantageous features of utilizing aLi₄Ti₅O₁₂ active material on a negative current collector made ofaluminum as opposed to a negative current collector made of copper. Inall cases described below, the negative electrodes were cycled againstpositive electrodes having a LiCoO₂ active material having a capacity of14.1 mAh.

A negative electrode was produced by mixing lithium titanate(commercially available from Süd Chemie Corporation) withpoly(vinylidine flouride) binder, carbon black and 1-methyl-2-pyrolidone(NMP) into a slurry and depositing the slurry onto an aluminum foilcurrent collector and drying on a heated drum. The active weight percentof the dried coating was 89.25%. The coating deposition level was 18.78mg/cm². The active area of the electrode was 5.04 cm². Based on thetheoretical specific capacity of Li₄Ti₅O₁₂ (155 mAh/g), the capacity ofthis electrode was 13.1 mAh.

A battery was assembled by combining the above-mentioned negative andpositive electrodes, spaced by a microporous separator, inside of ahermetic stainless steel can. The negative electrode was welded onto theinside of the can, and the positive electrode was connected to a anelectrical feedthrough. A lithium reference electrode was placed on theend of a second feedthrough pin, such that the lithium was located inthe headspace of the cell. A polyolefin spacer was placed inside thecan, parallel to the positive electrodes, to maintain uniform contactacross the entire electrode surface. The cell was activated by fillingwith electrolyte consisting of 1 M LiPF₆ in a mixture of propylenecarbonate, ethylene carbonate and diethyl carbonate.

The battery was cycled by charging and discharging at a current of 0.5mA using an ARBIN BT2000 battery cycler. For the first four cycles, thecell was cycled over a typical operational voltage range (charge to 3.0volts, discharge to 1.8 volts). Next, the cell was subjected to fouroverdischarge steps consisting of a normal charge followed byoverdischarge to 0 volts. The overdischarge took place as a sequence ofgalvanostatic steps, as follows: 0.5 mA down to 1.8 volts, 0.125 mA downto 1.0 volts, 0.05 mA down to 0 volts. After the overdischarge steps,the cell was again charged and discharged per the original method. Anauxiliary voltage measuring channel was used to record the potential ofthe negative electrode versus the lithium reference electrode. Thepotential of the positive electrode was obtained by summing the totalbattery voltage with the auxiliary voltage.

FIG. 6 shows three voltage traces for the cell. Curve 630 is the totalcell voltage, curve 620 is the positive electrode (versus Li reference)and curve 610 is the negative electrode (versus Li reference). Duringnormal cycling, the potential of the negative electrode ranges betweenabout 1.2 and 2.1 volts. However, during overdischarge, the potential ofthe negative electrode increases until it meets the potential of thepositive electrode. The two electrodes meet at a potential ofapproximately 3.9 volts. At this point, known as the “zero-volt crossingpotential,” the cell voltage (defined as the difference between thepositive and negative electrode potentials) is 0 volts. If this cellwere to have been made using a copper current collector for the negativeelectrodes, it is expected that the copper would have corroded, because3.9 volts is several hundred millivolts more anodic than the corrosionpotential of copper (approximately 3.5 volts).

A battery was fabricated and tested using methods identical to thosedescribed above. The battery utilized a negative electrode including agraphitized carbon active material on a copper current collector. FIG. 7shows the voltage traces for this battery (i.e., curve 710 is the totalcell voltage, curve 720 is the positive electrode (versus Li reference)and curve 730 is the negative electrode (versus Li reference)). Duringthe overdischarge cycle, the potential of the negative electrode wasnever above approximately 3.5 volts. It is believed that the reason forthis is that at this point, the copper current collector was freelycorroding, with the driving force for the corrosion reaction beingsupplied by the positive electrode.

According to an exemplary embodiment, lithium-ion batteries such asthose described above may be used in conjunction with medical devicessuch as medical devices that may be implanted in the human body(referred to as “implantable medical devices” or “IMD's”).

FIG. 8 illustrates a schematic view of a system 400 (e.g., animplantable medical device) implanted within a body or torso 432 of apatient 430. The system 400 includes a device 410 in the form of animplantable medical device that for purposes of illustration is shown asa defibrillator configured to provide a therapeutic high voltage (e.g.,700 volt) treatment for the patient 430.

The device 410 includes a container or housing 414 that is hermeticallysealed and biologically inert according to an exemplary embodiment. Thecontainer may be made of a conductive material. One or more leads 416electrically connect the device 410 and to the patient's heart 420 via avein 422. Electrodes 417 are provided to sense cardiac activity and/orprovide an electrical potential to the heart 420. At least a portion ofthe leads 416 (e.g., an end portion of the leads shown as exposedelectrodes 417) may be provided adjacent or in contact with one or moreof a ventricle and an atrium of the heart 420.

The device 410 includes a battery 440 provided therein to provide powerfor the device 410. According to another exemplary embodiment, thebattery 440 may be provided external to the device or external to thepatient 430 (e.g., to allow for removal and replacement and/or chargingof the battery). The size and capacity of the battery 440 may be chosenbased on a number of factors, including the amount of charge requiredfor a given patient's physical or medical characteristics, the size orconfiguration of the device, and any of a variety of other factors.According to an exemplary embodiment, the battery is a 5 mAh battery.According to another exemplary embodiment, the battery is a 300 mAhbattery. According to various other exemplary embodiments, the batterymay have a capacity of between approximately 10 and 1000 mAh.

According to other exemplary embodiments, more than one battery may beprovided to power the device 410. In such exemplary embodiments, thebatteries may have the same capacity or one or more of the batteries mayhave a higher or lower capacity than the other battery or batteries. Forexample, according to an exemplary embodiment, one of the batteries mayhave a capacity of approximately 500 mAh while another of the batteriesmay have a capacity of approximately 75 mAh.

According to another exemplary embodiment shown in FIG. 9, animplantable neurological stimulation device 500 (an implantable neurostimulator or INS) may include a battery 502 such as those describedabove with respect to the various exemplary embodiments. Examples ofsome neuro stimulation products and related components are shown anddescribed in a brochure titled “Implantable Neurostimulation Systems”available from Medtronic, Inc.

An INS generates one or more electrical stimulation signals that areused to influence the human nervous system or organs. Electricalcontacts carried on the distal end of a lead are placed at the desiredstimulation site such as the spine or brain and the proximal end of thelead is connected to the INS. The INS is then surgically implanted intoan individual such as into a subcutaneous pocket in the abdomen,pectoral region, or upper buttocks area. A clinician programs the INSwith a therapy using a programmer. The therapy configures parameters ofthe stimulation signal for the specific patient's therapy. An INS can beused to treat conditions such as pain, incontinence, movement disorderssuch as epilepsy and Parkinson's disease, and sleep apnea. Additionaltherapies appear promising to treat a variety of physiological,psychological, and emotional conditions. Before an INS is implanted todeliver a therapy, an external screener that replicates some or all ofthe INS functions is typically connected to the patient to evaluate theefficacy of the proposed therapy.

The INS 500 includes a lead extension 522 and a stimulation lead 524.The stimulation lead 524 is one or more insulated electrical conductorswith a connector 532 on the proximal end and electrical contacts (notshown) on the distal end. Some stimulation leads are designed to beinserted into a patient percutaneously, such as the Model 3487APisces-Quad® lead available from Medtronic, Inc. of Minneapolis Minn.,and stimulation some leads are designed to be surgically implanted, suchas the Model 3998 Specify® lead also available from Medtronic.

Although the lead connector 532 can be connected directly to the INS 500(e.g., at a point 536), typically the lead connector 532 is connected toa lead extension 522. The lead extension 522, such as a Model 7495available from Medtronic, is then connected to the INS 500.

Implantation of an INS 520 typically begins with implantation of atleast one stimulation lead 524, usually while the patient is under alocal anesthetic. The stimulation lead 524 can either be percutaneouslyor surgically implanted. Once the stimulation lead 524 has beenimplanted and positioned, the stimulation lead's 524 distal end istypically anchored into position to minimize movement of the stimulationlead 524 after implantation. The stimulation lead's 524 proximal end canbe configured to connect to a lead extension 522.

The INS 500 is programmed with a therapy and the therapy is oftenmodified to optimize the therapy for the patient (i.e., the INS may beprogrammed with a plurality of programs or therapies such that anappropriate therapy may be administered in a given situation). In theevent that the battery 502 requires recharging, an external lead (notshown) may be used to electrically couple the battery to a chargingdevice or apparatus.

A physician programmer and a patient programmer (not shown) may also beprovided to allow a physician or a patient to control the administrationof various therapies. A physician programmer, also known as a consoleprogrammer, uses telemetry to communicate with the implanted INS 500, soa clinician can program and manage a patient's therapy stored in the INS500, troubleshoot the patient's INS 500 system, and/or collect data. Anexample of a physician programmer is a Model 7432 Console Programmeravailable from Medtronic. A patient programmer also uses telemetry tocommunicate with the INS 500, so the patient can manage some aspects ofher therapy as defined by the clinician. An example of a patientprogrammer is a Model 7434 Itrel® 3 EZ Patient Programmer available fromMedtronic.

While the medical devices described herein (e.g., systems 400 and 500)are shown and described as a defibrillator and a neurologicalstimulation device, it should be appreciated that other types ofimplantable medical devices may be utilized according to other exemplaryembodiments, such as pacemakers, cardioverters, cardiac contractilitymodules, drug administering devices, diagnostic recorders, cochlearimplants, and the like for alleviating the adverse effects of varioushealth ailments. According to still other embodiments, non-implantablemedical devices or other types of devices may utilize batteries as areshown and described in this disclosure.

It is also contemplated that the medical devices described herein may becharged or recharged when the medical device is implanted within apatient. That is, according to an exemplary embodiment, there is no needto disconnect or remove the medical device from the patient in order tocharge or recharge the medical device. For example, transcutaneousenergy transfer (TET) may be used, in which magnetic induction is usedto deliver energy from outside the body to the implanted battery,without the need to make direct physical contact to the implantedbattery, and without the need for any portion of the implant to protrudefrom the patient's skin. According to another exemplary embodiment, aconnector may be provided external to the patient's body that may beelectrically coupled to a charging device in order to charge or rechargethe battery. According to other exemplary embodiments, medical devicesmay be provided that may require removal or detachment from the patientin order to charge or recharge the battery.

It is important to note that the construction and arrangement of thelithium-ion battery as shown and described with respect to the variousexemplary embodiments is illustrative only. Although only a fewembodiments of the present inventions have been described in detail inthis disclosure, those skilled in the art who review this disclosurewill readily appreciate that many modifications are possible (e.g.,variations in sizes, dimensions, structures, shapes and proportions ofthe various elements, values of parameters, mounting arrangements, useof materials, colors, orientations, etc.) without materially departingfrom the novel teachings and advantages of the subject matter recited inthe claims. Accordingly, all such modifications are intended to beincluded within the scope of the present invention as defined in theappended claims. Other substitutions, modifications, changes andomissions may be made in the design, operating conditions andarrangement of the preferred and other exemplary embodiments withoutdeparting from the scope of the present invention as expressed in theappended claims.

1. A lithium-ion battery comprising: a positive electrode comprising aLiCoO₂ active material; a polymeric separator configured to allowelectrolyte and lithium ions to flow between a first side of theseparator and an opposite second side of the separator; a liquidelectrolyte comprising a lithium salt dissolved in at least onenon-aqueous solvent; a negative electrode comprising a lithium titanateactive material; wherein the positive electrode has a first capacity andthe negative electrode has a second capacity that is less than the firstcapacity.
 2. The lithium-ion battery of claim 1, wherein the lithiumtitanate material comprises Li₄Ti₅O₁₂.
 3. The lithium-ion battery ofclaim 1, wherein the ratio of the second capacity to the first capacityis 0.85.
 4. The lithium-ion battery of claim 1, wherein the ratio of thesecond capacity to the first capacity is 0.93.
 5. The lithium-ionbattery of claim 1, wherein edges of the negative electrode do notextend beyond adjacent edges of the positive electrode.
 6. Thelithium-ion battery of claim 1, wherein the positive electrode and thenegative electrode each include foil current collectors.
 7. Thelithium-ion battery of claim 6, wherein the foil current collector of atleast one of the positive electrode and the negative electrode comprisesaluminum.
 8. The lithium-ion battery of claim 1, wherein the LiCoO₂active material of the positive electrode further comprises a binder anda conductive additive.
 9. The lithium-ion battery of claim 1, whereinthe battery has a nonhermetic construction.
 10. The lithium-ion batteryof claim 1, further comprising a battery housing that comprisesaluminum.
 11. The lithium-ion battery of claim 1, wherein the positiveelectrode and the negative electrode have a zero voltage crossingpotential above the decomposition potential of the active material ofthe positive electrode.
 12. The lithium-ion battery of claim 1, whereinthe separator comprises a polyolefin material.
 13. A lithium-ion batterycomprising: a positive electrode having a first capacity and comprisinga foil current collector and a LiCoO₂ active material; a polymericseparator; a liquid electrolyte; and a negative electrode having asecond capacity that is not greater than the first capacity, thenegative electrode comprising a foil current collector and a lithiumtitanate active material.
 14. The lithium-ion battery of claim 13,wherein the lithium titanate active material comprises Li₄Ti₅O₁₂. 15.The lithium-ion battery of claim 13, wherein the second capacity is lessthan the first capacity.
 16. The lithium-ion battery of claim 13,wherein the ratio of the second capacity to the first capacity is 0.85.17. The lithium-ion battery of claim 13, wherein the ratio of the secondcapacity to the first capacity is 0.93.
 18. The lithium-ion battery ofclaim 13, wherein at least one edge of the negative electrode does notextend beyond an adjacent edge of the positive electrode.
 19. Thelithium-ion battery of claim 13, further comprising a porous polymericseparator provided between the positive electrode and the negativeelectrode.
 20. The lithium-ion battery of claim 13, wherein the liquidelectrolyte comprises a lithium salt dissolved in at least onenon-aqueous solvent.
 21. The lithium-ion battery of claim 20, whereinthe electrolyte comprises LiPF₆ and at least non-aqueous solventselected from the group consisting of propylene carbonate, ethylenecarbone, and diethylene carbonate.
 22. The lithium-ion battery of claim13, wherein the current collector of the negative electrode comprisesaluminum.
 23. The lithium-ion battery of claim 13, wherein the currentcollector of the negative electrode comprises at least one materialselected from the group consisting of silver and titanium.
 24. Thelithium-ion battery of claim 23, wherein the positive current collectorcomprises aluminum.
 25. The lithium-ion battery of claim 13, wherein thebattery is nonhermetic.
 26. The lithium-ion battery of claim 13, furthercomprising a battery case in contact with the negative electrode, thebattery case comprising aluminum.
 27. The lithium-ion battery of claim13, wherein the active material of the negative electrode furthercomprises carbon and a poly(vinylidine fluoride) binder.
 28. Alithium-ion battery comprising: a positive electrode having a firstcapacity and comprising a foil current collector and an active materialcomprising LiCoO₂, a binder, and a conductive additive; a liquidelectrolyte; a negative electrode having a second capacity that is notgreater than the first capacity, the negative electrode comprising afoil current collector and a Li₄Ti₅O₁₂ active material; and a porouspolymeric separator provided between the positive electrode and thenegative electrode.
 29. The lithium-ion battery of claim 28, wherein theratio of the second capacity to the first capacity is 0.85.
 30. Thelithium-ion battery of claim 28, wherein the ratio of the secondcapacity to the first capacity is 0.93.
 31. The lithium-ion battery ofclaim 28, wherein at least one edge of the negative electrode does notextend beyond an adjacent edge of the positive electrode.
 32. Thelithium-ion battery of claim 28, wherein the electrolyte comprises LiPF₆and at least one material selected from the group consisting ofpropylene carbonate, ethylene carbone, and diethylene carbonate.
 33. Thelithium-ion battery of claim 28, wherein the negative electrodecomprises an aluminum current collector.
 34. The lithium-ion battery ofclaim 28, wherein the battery is nonhermetic.
 35. The lithium-ionbattery of claim 28, wherein the positive electrode and the negativeelectrode have zero voltage below a corrosion potential of the aluminumcurrent collector of the negative electrode.
 36. The lithium-ion batteryof claim 28, further comprising a polymeric separator providedintermediate the positive electrode and the negative electrode.
 37. Thelithium-ion battery of claim 28, further comprising a battery housing incontact with the negative electrode, the battery housing comprisingaluminum.
 38. The lithium-ion battery of claim 28, wherein the separatoris configured to allow the electrolyte and lithium ions to flow throughthe separator.